1. Field of the Invention
The present invention relates to a multilayer resist structure suitable for manufacturing a three-dimensional microstructure in MEMS (Micro Electro Mechanical Systems) and a method for manufacturing a three-dimensional microstructure with use of the multilayer resist structure.
2. Description of the Related Art
In recent years, with a demand for a scale-down of a semiconductor integrated circuit, a method for manufacturing a three-dimensional microstructure, such as a multilevel intersection in the case of, for example, wiring, with stability is required.
According to the related art, such a three-dimensional microstructure has been manufactured by using a multilayer resist structure. A multilayer resist structure is comprised of resist (photoresist) layers laid one upon another. After a multilayer resist structure is formed on a substrate, the film thicknesses in the multilayer resist structure are controlled part-to-part by selectively exposing the structure according to a desired pattern and selectively removing the resist layers by dry-etching. Then, wiring structures and the like are constructed by using the multilayer resist structure. Another method to control the film thicknesses of resist layers part-to-part is to selectively irradiate a single-layered resist with light of different intensity according to a desired pattern (refer to, for example, Digest of Papers Microprocesses and Nanotechnology 1998, p. 87-88, by Chang-Wook Beak and Yong-Kweon Kim).
However, with the related art mentioned above, it is very difficult to control the film thicknesses of resist layers part-to-part. For example, in the former method, the film thicknesses in a multi-layered resist are controlled by using differences in etching speed of dry-etching between the resist layers. Exact control over the film thicknesses part-to-part is not possible because of the variation in etching speed from lot to lot. As a result, a three-dimensional microstructure with high precision cannot be formed.
On the other hand, in the method of controlling the film thicknesses part-to-part by irradiating a single-layered resist with light of different intensity (or quantity of light), a slight variation in light intensity (or quantity of light) may result in a variation in depth of the developed pattern. Therefore, exact control over the film thicknesses can not be executed by this method either.
The invention has been made in view of the above-described problems. An object of the invention is to provide a multilayer resist structure which enables exact control over the film thicknesses part-to-part after exposure and development, and enables forming a three-dimensional microstructure with high precision.
Another object of the invention is to provide a method for manufacturing a three-dimensional microstructure, which enables forming a three-dimensional microstructure with high precision by using the multi-layer resist structure.
A multilayer resist structure according to the invention comprises a plurality of resist layers laid one upon another with an absorption layer capable of absorbing beams for exposure sandwiched between each two of the resist layers. For an absorption layer, an amorphous semiconductor such as amorphous silicon, a polycrystal semiconductor such as polycrystal silicon, amorphous carbon or the like is used. A resist as used herein refers to not only photoresist but also electron-sensitive resin. A beam for exposure as used herein refers to not only light such as ultraviolet rays but also electronic beam.
A method for manufacturing a three-dimensional microstructure according to the invention uses the multilayer resist structure. Specifically, in the method, the intensity or the irradiation quantity of the beam for exposure applied to the multilayer resist structure is altered according to a desired pattern. Especially, when absorption layer is formed of amorphous silicon or polycrystal silicon, it is possible to perform patterning while removing the absorption layers together with the resist layers with a developing solution.
In the multilayer resist structure according to the invention, an absorption layer capable of absorbing beams for exposure is sandwiched between each two of the resist layers. As a result, excess beams are prevented from being transmitted to a resist layer under the absorption layer at the time of exposure, and the film thicknesses after exposure and development become stable part-to-part. Furthermore, with the method for manufacturing a three-dimensional microstructure according to the invention, the multilayer resist structure according to the invention is used. Therefore, a stable three-dimensional microstructure can be formed.
Other and further objects, features and advantages of the invention will appear more fully from the following description.